WATERLOO, Iowa — Republican candidates learn a lot on the trail when they're competing in Iowa's first-in-the-nation presidential caucuses. Along with the sanctity of ethanol and the primacy of pork products, they eventually grasp this is Sen. Charles E. Grassley's state. When you run for president here, at some point, Iowa's senior senator will appear alongside you, and everyone knows who he is.

"I didn't know Grassley was going to show up," said Bill Davidson, a bartender at The Supervisors Club, where the senator was introducing New Jersey Gov. Chris Christie. Davidson sounded impressed, as if the event, being repeated over and over throughout the state in the run-up to Monday's caucuses, had been elevated.

He shouldn't have been surprised. Every year, the Republican senator makes a point of visiting all of the Hawkeye State's 99 counties — what's referred to as the "Full Grassley." With the state full of presidential candidates traversing Iowa for votes, Grassley planned events with each one, though he did not endorse any of them.

As Davidson poured Bloody Marys, as well as some non-alcoholic beverages for the crowd the afternoon of Jan. 30, Grassley worked the room, taking selfies, conferring with Christie's staff and talking about the relatively balmy (for Iowa in January at least) 40-degree day. Christie was late, and even after arriving, talked on his cell phone in the parking lot. That gave Grassley more time to kibitz.

"I'd take a picture with you even if you didn't vote for me!" he said to a man who joked since he voted for the senator, he he hoped he could get a photo. "Maybe someone like Putin I wouldn't," Grassley joshed.

Grassley was on a tight schedule. The Christie event was scheduled to start at 3 p.m., and the senator had a 4 p.m. event in nearby Cedar Falls at the Fraternal Order of Eagles Aerie 4074 with former Florida Gov. Jeb Bush.

"My gosh! You're here!" Grassley said when Christie did eventually amble in around 3:30 p.m. The two exchanged quick pleasantries, Grassley introduced the governor, recounting that "I had the privilege of voting for him as U.S. attorney" when Christie's appointment to U.S. attorney for New Jersey had to be confirmed by the Senate. He then stayed for a few minutes more to hear Christie say Grassley would be one of the first on an "Iowa Republican Mount Rushmore." Then Grassley bolted for the Bush event.

First elected to the Senate in 1980, Grassley is up for re-election to a sixth term in November. He'll be 82 in September, and he shows few signs of slowing down. That's despite the fact he has no primary opponent, and the Democrats exploring runs against him don't pose much of a threat, at least at this point. After votes on Jan. 28, he returned home with plans to stump for nine GOP candidates before Monday night's caucuses.

At the first of those events, Friday morning in Cedar Rapids for Ohio Gov. John Kasich, Iowa Republican Party Chairman Jeff Kaufmann introduced Grassley as "Mr. Iowa himself."

"No office belongs to any one person," Grassley told the folks gathered in the National Czech and Slovak Museum and Library's Mitvalsky Room. "You have to renew that public trust from time to time."

When Kasich followed, he praised Grassley as a polite "pit bull" and, without explicitly stating the Iowa senator was running for re-election in November, said, "Why don't we just not have an election. Let's do it by acclimation."

Grassley has a standard introductory speech, written out on a piece of paper he clutches at each event. It contains GOP red meat about taxes, regulation, spending, telling it like it is, preventing a "third term of the Obama presidency" and the like. He customizes for each crowd. But he always returns to the need to stay motivated going into November. "This enthusiasm has to keep up," he told a Ben Carson crowd at the University of Iowa Athletic Club in Iowa City a couple of hours after the Kasich event.

Candidate after candidate lauded Grassley's work ethic, his record-breaking streak of not missing a Senate vote in more than 22 years, and his reputation for straight talk. All of them except Carson, who simply said, "Thank you, Sen. Grassley." Then he began his own speech: "I'm absolutely delighted to be here today, after the debate last night in which I didn't get a lot of time, but I did get a chance to say a lot."

That might have been the exception, but the senator stayed to listen to most of Carson's approximately 45 minute speech — aside from a few moments when he ran out of the room because his phone rang. His next event wasn't for a few more hours in Wilton, 35 miles away.

At that next event — Eventbrite identified it as "Cruzin' to Caucus — Wilton, IA Town Hall with Senator Ted Cruz and Special Guest Senator Chuck Grassley" — Grassley found a crowd gathered at Wilton's modern library and community center off a dirt road and amid farmland in Eastern Iowa.

"This man is special. This man is a leader in the United States Senate," Cruz said about Grassley, who acknowledged the Texan with a thumbs-up, and promptly headed for the exit. It had been a long day, and six more events were scheduled on Saturday, Sunday and Monday before the caucuses.

Throughout his appearances, Grassley never mentioned his own re-election plans. He stuck to the presidential race, taking shots at Democrats, and extolled the need to stay enthusiastic.

"What a crowd!" he said at his third event of Jan. 30, a rally for Sen. Marco Rubio at, perhaps appropriately for a Floridian, the Ramada Tropics Conference Center in Urbandale. "What a crowd!" he repeated, after drinking a can of sugar-free Red Bull before taking the stage.

Rubio then made sure the audience knew about Grassley's race. "There is no one who does a better job representing their state," Rubio said, adding, "This year, he's up for re-election. You better send him back!"

And as the state prepares for Monday's political ritual, it's interesting to note Grassley won't be able to partake in it himself. The irony of being someone who doesn't miss votes means he won't be caucusing in his beloved state come Monday evening.

The Senate, you see, has votes scheduled that day, and the one thing Grassley doesn't plan on doing anytime soon is missing one of those.